Numerous inventions have been proposed over the past one hundred years to reduce water consumption in toilets. They commonly use a mechanism that sustains the valve in an open position until the tank is partly drained. They then close the valve early to conserve the remaining water. Many of them have two flush levels. A short flush uses a small amount of water to flush out liquid waste. A longer flush drains most of the tank to flush out solid waste.
Despite the increasing need for water conservation, these water-saving flush valves have not had commercial success. This is because they nearly all have one common problem. They cause the toilet bowl not to refill to its normal level. This is due to the following two reasons:
a) In conventional toilets the rate of flow decreases gradually as the tank empties. When the flow rate becomes too slow the flushing action stops. The valve is not yet closed and the remaining water coming down from the tank contributes to refilling the bowl. In contrast, water-saving valves close quickly while the flow is still strong. No more water comes down to help refill the bowl. The momentum of water in the bowl and the siphoning action pull nearly all the water out of the bowl.
b) The bowl is normally refilled from the same ball cock that refills the tank. The refill water runs through a small hose from the ball cock to the top of the overflow tube. Less time is required to refill a partly empty tank after a water-saving flush than is required to refill an empty tank. Therefore there is less time available to refill the bowl.
A properly-filled toilet bowl is not just for looks. When the bowl has less water in it the toilet does not flush as well as it otherwise could. The first portion of water coming down from the tank only fills the bowl up to the level of the siphon. By the time water starts running out the siphon there is less water in the tank. The tank is draining more slowly. With the flow rate slower, a larger quantity of water is required to start the siphoning action which causes the flush. Overall, the toilet is then less efficient. If the flow rate is too slow or too short the siphoning action will not start at all. The toilet will not flush and the contents of the bowl are only diluted.
Very few of the previous water-saving inventions have proposed a method for refilling the bowl to its proper level. The methods that were proposed were too complex and expensive. A professional would be needed to install them. An example of this is U.S. Pat. No. 3,744,064 (Preston, Jul. 10, 1973). It uses two specialized control valves along with an array of tubes and a piston.
A simple method was proposed in U.S. Pat. No. 4,922,556 (Roosa, May 8, 1990). It uses a small hole in the overflow tube near the top. After the ball cock shuts off water continues to run through the hole to refill the bowl. The hole must be about two inches below the highest water level to allow sufficient water to refill the bowl. However, most ball cocks will turn back on before the water gets that low. Methods like this are unreliable for another reason. If pressure at times becomes too low in the supply line, water runs through the hole as fast as the tank is refilled. The water level never gets high enough to shut off the ball cock and the water runs continuously.
A ball cock could be made to divert more water through the hose to the overflow tube to refill the bowl. It could be sold with the new water-saving flush valve. However that would greatly increase the cost of the water-saving system. It would also be more troublesome to install. It would waste water on two-level systems by sending too much water to the bowl during the longer flush.